<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>rem布局准备工作</title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    html {
      font-size: 20px;
    }

    .box {
      width: 37.5rem;
      height: 5rem;
      background: yellow;
    }
  </style>
  <script>
    //fontsize 计算
    document.documentElement.style.fontSize = document.documentElement.clientWidth / 750 * 16 + 'px'

        //fontsize = 当前设备的css布局宽度/物理分辨率（设计稿的宽度）*基准font-size
  </script>
</head>

<body>
  <div class="box">
    赵钱孙李
  </div>
</body>

</html>